Riprap Calculator
A riprap calculator estimates stone volume and US short tons from covered area and blanket thickness. This calculator uses a generic placed density of 130 lb/ft³, including voids. Enter dimensions along the covered surface, including slope distance where needed, rather than substituting horizontal plan width.
Riprap tonnage
97.5tons
- Area
- 1,000.00 SF
- Volume before allowance
- 55.56 CY
Formula: tons = length ft × slope width ft × (thickness in ÷ 12) × 130 lb/ft³ ÷ 2,000 lb, then + waste %
Uses a generic density from the site’s material table. Confirm a product-specific value with the supplier.
How the calculation works
Multiply length by the width along the surface to get covered area. Multiply by blanket thickness converted to feet. The result divided by 27 is cubic yards; multiplied by 130 and divided by 2,000 is short tons. The allowance increases tonnage only.
For a simple slope, face length is the square root of horizontal run squared plus vertical rise squared. A 2H:1V slope has a face length about 1.118 times its horizontal run. This widget does not calculate slope length for you; convert the dimensions before entering them.
For example, 100 feet by 10 feet of surface coverage at 18 inches thickness is 1,500 cubic feet, or 55.56 cubic yards. At 130 lb/ft³, that is 97.5 tons before allowance.
Use the specified rock class and blanket thickness. Separate toe trenches, transitions, filter layers, and irregular sections from the main blanket calculation. The generic density does not select a rock gradation or verify hydraulic performance.
Reference values
| Quantity | Value | Basis |
|---|---|---|
| Riprap, placed blanket | 130 lb/ft³ | generic unit weight, voids included |
| Tons per cubic yard | ≈ 1.76 | 130 × 27 ÷ 2,000 |
| Slope length on 2:1 | ≈ 1.118 × horizontal | geometry of the slope |
| Slope length on 3:1 | ≈ 1.054 × horizontal | geometry of the slope |
Frequently asked questions
Should width come from the plan view?
Only if the covered surface is horizontal. On a slope, enter the distance along the slope face.
How many tons are in a cubic yard of riprap?
At the generic placed density used here, 27 × 130 ÷ 2,000 = 1.755 short tons per cubic yard.
Does it include a toe trench or filter layer?
No. Calculate those separately from their own dimensions and material requirements.
Does the calculator choose a riprap class?
No. Stone class and blanket thickness must come from the design or project specification.